Trying to get RaycastVehicle to work

[SiWi]

My current setup is very similar to the setup in the Demo with two expections:
1. I'm using a standard box shape as ground
2. I'm using the btVehicleTuning's standard values
My car is falling down a few metres until it hits the box surface. If I wait until it's resting on the ground, I won't be able to move it afterwards by applying engine force-> it's stuck.
When I apply engine force while it's falling down I can get it to drive on the box regularly, but as soon as I break to zero speed it will get stuck or start to roll backwards slowly.

What could be my mistake? Is the Boxshape the problem?
EDIT1: When using the demo's settings for the wheels the car will start to fly up straight without applying any engine force.
EDIT2: With default settings the car is driving as expected for a short period of time, but starts flip away from the ground and getting out of control at some random point.

[SiWi]

By setting the center of mass to a low position and using the default settings I at least managed to get my car sticking to the ground. My current problem is that the car is much too slidey and the general behaviour in curves seems to be unrealistic. By the way: What scale does the steering value use?